A polymer gel electrolyte composition includes a crosslinked polymer network matrix having a three-dimensional crosslinked structure that includes a solution of an electrolyte in a non-aqueous solvent, and a non-crosslinked polymer included within the crosslinked polymer network matrix. The non-crosslinked polymer includes (a) an ethylene unit and/or propylene unit, and (b) an unsaturated carboxylic acid unit having a carboxyl group esterified by a polyalkylene glycol having one terminal hydroxyl group protected.